The subject matter disclosed herein relates generally to photoacoustic imaging and, more specifically, to using photoacoustic tomography to characterize a target or targeted area within a tissue.
At least some known photoacoustic imaging systems provide high-quality images using a hand-held scanning probe. From an instrumentation point of view, photoacoustic imaging relies heavily on ultrasound detection technology. As such at least some known photoacoustic imaging systems have largely focused on customized ultrasound transducers or scanning systems. However, such photoacoustic imaging systems do not include real-time mechanical scanning capabilities.
For example, at least one known ultrasound-based high-resolution in vivo micro-imaging system uses a single-element scanning ultrasonic imaging platform. Such a system has the ability to visualize in real time and quantify animal anatomical targets, hemodynamics (blood flow), and therapeutic interventions with resolution down to approximately 30 microns. Moreover, such a system includes a power Doppler capability to visualize and quantify relative blood flow in vivo for anti-angiogenic studies. Using such a system enables acquisition of at least 100 frames per second (fps). Further, such a system may be used for high-resolution imaging within a depth of ˜20 mm which diffuse light can still penetrate.
However, while ultrasonic imaging is primarily based on acoustic impedance inhomogeneity, photoacoustic imaging is based on optical absorption contrast, which is as strong as 5000% between blood or melanin and the surrounding tissue at some optical wavelengths and contains information about tissue molecular composition or physiological status (e.g., blood oxygenation). Therefore, optical and ultrasonic contrasts are complementary and optical contrasts can open new possibilities for in vivo imaging. For example, the combination of the above-described system's ability to measure blood velocity and photoacoustic imaging's ability to measure blood oxygenation as well as blood hemoglobin concentration makes possible real-time measurements of tissue metabolic rate. Moreover, photocacoustic imaging may help such an ultrasonic imaging system identify certain light absorbing structures such as blood vessels or melanin-rich melanomas and to use optical absorption based contrast agents such as nanostructures or FDA approved indocyanine green (ICG) dye for molecular imaging. With the help of dye, photocacoustic imaging may also be used to identify sentinel lymph nodes.
Accordingly, a method and apparatus is desirable that combines ultrasound-based high-resolution in vivo micro-imaging systems, such as those described above, with photoacoustic imaging using a flexibly mounted cantilever beam.